1. Field of the Invention
The present invention relates to memories, and more particularly, to resistive memories.
2. Description of the Related Art
Examples of nonvolatile memories using resistance materials include resistive random access memories (RRAMs), phase-change random access memories (PRAMs), and magnetic RAMs (MRAMs). Dynamic RAMs (DRAMs) or flash memories store data using charges. Nonvolatile memories using resistance materials store data by changing the resistance of a variable resistance material (in the case of RRAMs), changing the state of a phase change material such as a chalcogenide alloy (in the case of PRAMs), or changing the resistance of a magnetic tunnel junction (MTJ) thin film according to a magnetization state of a ferromagnetic material (in the case of MRAMs), and the like.
A resistive memory cell includes a variable resistance material between an upper electrode and a lower electrode, and the resistance level of the variable resistance material varies according to a voltage applied to the upper and lower electrodes. Examples of such resistive memory cells are discussed in U.S Patent Publication Nos. 2005-58009 and 2004-27849, the disclosures of which are hereby incorporated herein in their entirety by reference. In particular, a filament that serves as a current path for a cell current is formed in the variable resistance material. A state in which a part of the filament is disconnected is defined as a reset state, a high resistance state, or reset data (data 1). A state in which the filament is connected is defined as a set state, a low resistance state, or set data (data 0).
A reset voltage having a voltage level, at which the filament may be disconnected, is supplied to write reset data into resistive memory cells. A set voltage having a voltage level, at which the filament may be reconnected, is supplied to write set data into the resistive memory cells. Further, a voltage having a low voltage level, at which the state of the filament does not change, is supplied to read stored data so as to determine whether the read data is reset data or set data.